Configuring optical layers in imprint lithography processes

ABSTRACT

An imprint lithography method of configuring an optical layer includes selecting one or more parameters of a nanolayer to be applied to a substrate for changing an effective refractive index of the substrate and imprinting the nanolayer on the substrate to change the effective refractive index of the substrate such that a relative amount of light transmittable through the substrate is changed by a selected amount.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/859,584, filed on Apr. 27, 2020, which is a continuation of U.S.application Ser. No. 16/165,027, filed on Oct. 19, 2018, now U.S. Pat.No. 10,670,971, which claims the benefit of the filing date of U.S.Provisional Application No. 62/574,826, filed on Oct. 20, 2017. Thecontents of U.S. application Ser. Nos. 62/574,826, 16/165,027 and16/859,584 are incorporated herein by reference in their entirety.

TECHNICAL FIELD

This invention relates to configuring optical layers in imprintlithography processes, and more particularly to forming anti-reflectivefeatures on a substrate to tune light transmission through thesubstrate.

BACKGROUND

Nanofabrication (e.g., nanoimprint lithography) is the fabrication ofvery small structures that have features on the order of 100 nanometersor smaller. One application in which nanofabrication has had asignificant impact is in the processing of integrated circuits. Thesemiconductor processing industry continues to strive for largerproduction yields, while increasing a number of circuits formed on asubstrate per unit area of the substrate. To this end, nanofabricationhas become increasingly important to achieving desired results in thesemiconductor processing industry. Nanofabrication provides greaterprocess control while allowing continued reduction of minimum featuredimensions of structures formed on substrates. Other areas ofdevelopment in which nanofabrication has been employed includebiotechnology, optical technology, mechanical systems, and the like. Insome examples, nanofabrication includes fabricating structures onsubstrates that are assembled to form an optical device.

SUMMARY

The invention involves a realization that imprinting certain types ofnanoscale features on a substrate can significantly improve transmissionof light (e.g., source light and world side light) through thesubstrate. For example, anti-reflective (AR) patterns can be formed fromof nanoscale pillars, nanoscale holes, and nanoscale gratings thatdiminish light reflection losses at a substrate, thereby increasinglight transmission through the substrate. Depending on a size, a shape,an aspect ratio, and a pitch of the nanoscale features, lighttransmission through a substrate can be tuned to a desired level usingpatterned polymer films of index varying from 1.49 to 1.74. In thisregard, AR patterns formed on a substrate can also provide the substratewith a new effective refractive index. Such features can be imprintedwithin ultra thin films of less than 150 nm thickness, therebyconserving material use and further enabling use of stacked waveguidesusing thin imprinted layers over glass substrates. Nanoscale featuresbeing imprinted have an overall pitch and dimensions of less than 300nm, such that the nanoscale features do not cause unwanted diffractionor light scattering as light propagates through each layer in amulticolor waveguide stack. Such imprinted nanoscale features alsoenable higher transmission of world side light through each layer,thereby enhancing world side objects as viewed through a user's eye(e.g., pupil). Such nanoscale features can also act as dummy fillregions around edges of waveguide pattern geometry, enabling smoothtransition of resist fluid prior to curing through a patterned region toanother patterned region versus a patterned region to a blankun-patterned region. These nanoscale features are imprinted with a verythin residual layer thicknesses of less than 100 nm, which allows thepattern transfer into any underlying material layer or directly into thesubstrate to enhance the anti-reflective properties of that layer orjust the bare substrate, itself

One aspect of the invention features an imprint lithography method ofconfiguring an optical layer. The imprint lithography method includesselecting one or more parameters of a nanolayer to be applied to asubstrate for changing an effective refractive index of the substrateand imprinting the nanolayer on the substrate to change the effectiverefractive index of the substrate such that a relative amount of lighttransmittable through the substrate is changed by a selected amount

In some embodiments, the relative amount of light is a first relativeamount of light, and imprinting the nanolayer on the substrate to changethe effective refractive index of the substrate includes changing asecond relative amount of light reflected from a surface of thesubstrate.

In certain embodiments, the imprint lithography method further includesselecting one or more of a shape, a dimension, and a materialformulation of the nanolayer.

In some embodiments, the imprint lithography method further includesimprinting a flat nanoimprint on the substrate.

In certain embodiments, the imprint lithography method further includesimprinting a featured nanoimprint on the substrate.

In some embodiments, the imprint lithography method further includesimprinting one or more anti-reflective (AR) features on the substrate.

In certain embodiments, the one or more AR features have a height in arange of about 10 nm to about 300 nm.

In some embodiments, the one or more AR features have a width in a rangeof about 10 nm to about 150 nm.

In certain embodiments, the imprint lithography method further includesdistributing the one or more AR features with a pitch in a range ofabout 20 nm to about 200 nm.

In some embodiments, the imprint lithography method further includesforming pillars on the substrate.

In certain embodiments, the imprint lithography method further includesforming holes on the substrate.

In some embodiments, the imprint lithography method further includesforming one or both of continuous gratings and discontinuous gratings onthe substrate.

In certain embodiments, the imprint lithography method further includesforming a functional pattern on a first side of the substrate andimprinting the nanolayer along one or both of the first side of thesubstrate and a second side of the substrate opposite the first side ofthe substrate.

In some embodiments, the imprint lithography method further includesforming an array of AR features of the nanolayer along a specificdirection with respect to the functional pattern.

In certain embodiments, the imprint lithography method further includesforming the AR features of the nanolayer on the substrate to change theeffective refractive index of the substrate based on a direction oflight propagation such that light transmitted through the substrate ischanged by the selected amount.

In some embodiments, the imprint lithography method further includesapplying a film coating to the substrate and imprinting the nanolayeratop the film coating.

In certain embodiments, the imprint lithography method further includeschanging the relative amount of light transmittable through thesubstrate by about 0.5% to about 15%.

In some embodiments, the nanolayer is a first nanolayer, and the imprintlithography method further includes imprinting a second nanolayer atopthe first nanolayer.

In certain embodiments, the imprint lithography method further includeschanging the effective refractive index to a first value based on thefirst nanolayer and changing the effective refractive index to a secondvalue based on the second nanolayer.

Another aspect of the invention features an optical layer that includesa substrate and a nanolayer imprinted on the substrate, the nanolayerdetermining an effective refractive index of the substrate such that thenanolayer effects a relative amount of light transmittable through thesubstrate.

Another aspect of the invention features an optical device that includesa first optical layer and a second optical layer. The first opticallayer includes a first substrate and a nanolayer imprinted on the firstsubstrate. The second optical layer includes a second substrate, and afunctional pattern disposed along the second substrate. The nanolayerimprinted on the first substrate determines an effective refractiveindex of the first substrate such that the nanolayer increases arelative amount of light transmittable through the first substrate tothe second optical layer.

In some embodiments, the functional pattern disposed along the secondsubstrate is a first functional pattern, and the optical device furtherincludes a third optical layer including a third substrate and a secondfunctional pattern disposed along the third substrate.

In certain embodiments, the nanolayer imprinted on the first substrateis a first nanolayer, the effective refractive index of the firstsubstrate is a first refractive index, the relative amount of light is afirst relative amount of light, and the second optical layer includes asecond nanolayer imprinted on the second substrate, the second nanolayerdetermining a second effective refractive index of the second substratesuch that the second nanolayer increases a second relative amount oflight transmittable through the second substrate to the third opticallayer.

In some embodiments, the first and second nanolayers are configured suchthat a final amount of light transmitted through the first and secondsubstrates to the third optical layer is about equal to an amount oflight directed from a source to the first nanolayer, minus a firstamount of light reflected from the first substrate and minus a secondamount of light reflected from the second substrate.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,aspects, and advantages of the invention will be apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an imprint lithography system.

FIG. 2 is diagram of patterned layer formed by the imprint lithographysystem of FIG. 1.

FIG. 3 is a top view of an optical layer.

FIG. 4 is a side view of the optical layer of FIG. 3.

FIG. 5 is a top view of an optical layer.

FIG. 6 is a top view of an optical layer.

FIG. 7 is a side view of an optical layer.

FIG. 8 is a side view of an optical layer.

FIG. 9 is a side view of an optical layer.

FIG. 10 provides SEM images (a)-(d) illustrating side views of variousanti-reflective (AR) features.

FIG. 11 is a diagram illustrating effects of nanopatterns applieddirectly atop a substrate.

FIG. 12 is a diagram illustrating effects of stacking featurednanopatterns atop a substrate.

FIG. 13 is a graph of light transmission through a substrate withvarious treatments applied to the substrate.

FIG. 14 is a diagram illustrating a substrate with nanoimprint gratingsapplied in a same direction (a) and in a perpendicular direction (b) ascompared to a direction of diffraction gratings of a functional patternon the substrate.

FIG. 15 is a graph of light transmitted through a substrate with varioustreatments applied to the substrate.

FIG. 16 is a graph of light transmitted through a WGP substrate withvarious treatments applied to the WGP substrate.

FIG. 17 is a graph of indexes of refraction for various substratetreatments.

FIG. 18 is diagram illustrating light transmission through a multi-layeroptical device.

FIG. 19 is a diagram illustrating a light source directed towardsmultiple layers of a waveguide eye-piece that include a non-imprinted ARfilm.

FIG. 20 is a diagram illustrating a light source directed towardsmultiple layers of a waveguide eye-piece that include an imprinted ARnanolayer.

FIG. 21 is a flow chart of an example process for configuring an opticallayer in an imprint lithography process.

Like reference symbols in the various figures indicate like elements.

In some examples, illustrations shown in the drawings may not be drawnto scale.

DETAILED DESCRIPTION

An imprint lithography process for configuring an optical layer isdescribed below. The imprint lithography process involves formingnanoscale surface relief pattern anti-reflective (AR) imprints onsubstrates. Such AR imprints serve to increase light transmissionthrough the substrate to varying degrees, depending on various geometricproperties of the AR imprints.

FIG. 1 illustrates an imprint lithography system 100 that is operable toform a relief pattern on a top surface 103 of a substrate 101 (e.g., awafer). The imprint lithography system 100 includes a support assembly102 that supports and transports the substrate 101, an imprintingassembly 104 that forms the relief pattern on the top surface 103 of thesubstrate 101, a fluid dispenser 106 that deposits a polymerizablesubstance upon the top surface 103 of the substrate 101, and a robot 108that places the substrate 101 on the support assembly 102. The imprintlithography system 100 also includes one or more processors 128 that canoperate on a computer readable program stored in memory and that are incommunication with and programmed to control the support assembly 102,the imprinting assembly 104, the fluid dispenser 106, and the robot 108.

The substrate 101 is a substantially planar, thin slice that istypically made of one or more materials including silicon, silicondioxide, titanium dioxide, zirconium dioxide, aluminum oxide, sapphire,germanium, gallium arsenide (GaAs), an alloy of silicon and germanium,indium phosphide (InP), or other example materials. The substrate 101typically has a substantially circular or rectangular shape. Thesubstrate 101 typically has a diameter in a range of about 50 mm toabout 200 mm (e.g., about 65 mm, about 150 mm, or about 200 mm) or alength and a width in a range of about 50 mm to about 200 mm (e.g.,about 65 mm, about 150 mm, or about 200 mm). The substrate 101 typicallyhas and a thickness in a range of about 0.2 mm to about 1.0 mm. Thethickness of the substrate 101 is substantially uniform (e.g., constant)across the substrate 101. The relief pattern is formed as a set ofstructural features (e.g., protrusions and recesses) in thepolymerizable substance upon the top surface 103 of the substrate 101,as will be discussed in more detail below.

The support assembly 102 includes a chuck 110 that supports and securesthe substrate 101, an air bearing 112 that supports the chuck 110, and abase 114 that supports the air bearing 112. The base 114 is located in afixed position, while the air bearing 112 can move in up to threedirections (e.g., x, y, and z directions) to transport the chuck 110(e.g., in some instances, carrying the substrate 101) to and from therobot 108, the fluid dispenser 106, and the imprinting assembly 104. Insome embodiments, the chuck 110 is a vacuum chuck, a pin-type chuck, agroove-type chuck, an electromagnetic chuck, or another type of chuck.

Still referring to FIG. 1, the imprinting assembly 104 includes aflexible template 116 with a patterning surface defining an originalpattern from which the relief pattern is formed complementarily on thetop surface 103 of the substrate 101. Accordingly, the patterningsurface of the flexible template 116 includes structural features, suchas protrusions and recesses. The imprinting assembly 104 also includesmultiple rollers 118, 120, 122 of various diameters that rotate to allowone or more portions of the flexible template 116 to be moved in the xdirection within a processing region 130 of the imprint lithographysystem 100 to cause a selected portion of the flexible template 116 tobe aligned (e.g., superimposed) with the substrate 101 along theprocessing region 130. One or more of the rollers 118, 120, 122 areindividually or together moveable in the vertical direction (e.g., the zdirection) to vary a vertical position of the flexible template 116 inthe processing region 130 of the imprinting assembly 104. Accordingly,the flexible template 116 can push down on the substrate 101 in theprocessing region 130 to form an imprint atop the substrate 101. Anarrangement and a number of the rollers 118, 120, 122 can vary,depending upon various design parameters of the imprint lithographysystem 100. In some embodiments, the flexible template 116 is coupled to(e.g., supported or secured by) a vacuum chuck, a pin-type chuck, agroove-type chuck, an electromagnetic chuck, or another type of chuck.

In operation of the imprint lithography system 100, the flexibletemplate 116 and the substrate 101 are aligned in desired vertical andlateral positions by the rollers 118, 120, 122 and the air bearing 112,respectively. Such positioning defines a volume 124 within theprocessing region 130 between the flexible template 116 and thesubstrate 101. The volume 124 can be filled by the polymerizablesubstance once the polymerizable substance is deposited upon the topsurface 103 of the substrate 101 by the fluid dispenser 106, and thechuck 110 (e.g., carrying the substrate 101) is subsequently moved tothe processing region 130 by the air bearing 112. Accordingly, both theflexible template 116 and the top surface 103 of the substrate 101 canbe in contact with the polymerizable substance in the processing region130 of the imprint lithography system 100. Example polymerizablesubstances may be formulated from one or more substances, such asisobornyl acrylate, n-hexyl acrylate, ethylene glycol diacrylate,2-hydroxy-2-methyl-1-phenyl-propan-1-one,(2-Methyl-2-Ethyl-1,3-dioxolane-4-yl)methyl acrylate, hexanedioldiacrylate,2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone,diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide,2-hydroxy-2-methyl-1-phenyl-1-propanone, and various surfactants.Example techniques by which the polymerizable substance may be depositedatop the substrate 101 by the fluid dispenser 106 include drop dispense,spin-coating, dip coating, slot-die, knife-edge coating, micro-gravure,screen-printing, chemical vapor deposition (CVD), physical vapordeposition (PVD), thin film deposition, thick film deposition, and othertechniques. In some examples, the polymerizable substance is depositedatop the substrate 101 in multiple droplets.

The printing system 104 includes an energy source 126 that directsenergy (e.g., broadband ultraviolet radiation) towards the polymerizablesubstance atop the substrate 101 within the processing region 130.Energy emitted from the energy source 126 causes the polymerizablesubstance to solidify and/or cross-link, thereby resulting in apatterned layer that conforms to a shape of the portion of the flexibletemplate 116 in contact with the polymerizable substance in theprocessing region 130.

FIG. 2 illustrates an example patterned layer 105 formed on thesubstrate 101 by the imprint lithography system 100. The patterned layer105 includes a residual layer 107 and multiple features includingprotrusions 109 extending from the residual layer 107 and recessions 111formed by adjacent protrusions 109 and the residual layer 107.

While the imprint lithography system 100 is described and illustrated asa roll-to-plate or plate-to-roll system, imprint lithography systems ofdifferent configurations can also be used to produce the examplepatterned layer 105 and the example patterns discussed below. Suchimprint lithography systems may have a roll-to-roll or a plate-to-plateconfiguration.

In some embodiments, a substrate (e.g., the substrate 101 of the imprintlithography system 100) is processed (e.g., imprinted on one or bothsides, supplied with additional features, and/or cut out to shape) toform an optical layer of an optical device. For example, a nanolayer canbe imprinted on the substrate to enhance optical performances of thesubstrate, such as to increase or reduce a transmissivity of thesubstrate to light of certain wavelengths and/or to enhancebirefringence of the substrate. Example optical devices include opticalfilms (e.g., Wire Grid Polarizer (WGP) films) of high transmission(e.g., greater than 42%) and high Extinction Ratio (ER) (e.g., greaterthan 1000)) used in display applications (e.g., liquid crystal display(LCD) applications), touchscreen display applications (e.g., touchsensors), and to improve intensity of light transmitted from either sideof an optical film, such as in a wearable eyepiece, an optical sensor,or an optical film.

FIGS. 3 and 4 illustrate a top view and a side view, respectively, of anoptical layer 200 that includes a substrate 202 with an upper side 204and a lower side 206. The optical layer 200 also includes a functionalpattern 208 imprinted on the upper side 204 of the substrate 202, an ARpattern 210 imprinted on the upper side 204 of the substrate 202, a filmcoating 212 disposed on the lower side 206 of the substrate 202, and anAR pattern 214 imprinted on the film coating 212. The substrate 202 maybe laser cut from a larger substrate (e.g., the substrate 101) and isprovided as a layer of transparent or semi-transparent plastic (e.g., aflexible material) or glass (e.g., a rigid material) that is made of oneor more organic or inorganic materials, in accordance with the variousmaterial formulations described above with respect to the substrate 101.The substrate 202 may have a length of about 10 mm to about 150 mm(e.g., about 50 mm), a width of about 10 mm to about 150 mm (e.g., about50 mm), and a thickness of about 0.1 mm to about 10.0 mm (e.g., about0.3 mm). The substrate 202 has a relatively high refractive index in arange of about 1.6 to about 1.9 (e.g., about 1.8). Assuming that thesubstrate 202 is surrounded by air (i.e., n=1), the substrate 202 has atransmissivity (e.g., a portion of light impinging on the substrate 202that passes through the substrate 202) in a range of about 80.00% toabout 95.00% (e.g., about 91.84%) and accordingly has a reflectivity(e.g., the portion of light impinging on the substrate 202 that isreflected backwards from the substrate 202) of about 5.00% to about20.00% (e.g., about 8.16%).

The functional pattern 208 is imprinted (e.g., via the imprintlithography system 100) along an interior region 216 of the substrate202. The functional pattern 208 is a waveguide pattern formed ofmultiple diffraction gratings that provide a basic working functionalityof the optical layer 200. The diffraction gratings have dimensions in arange of about 10 nm to about 600 nm. The diffraction gratings areconfigured to project light of wavelengths within a particular range andto focus a virtual image at a particular depth plane. The focused light,together with focused light projected through proximal optical layers,forms a multi-color virtual image over one or more depth planes. Thetransmitted light may be red light with wavelengths in a range of about560 nm to about 640 nm (e.g., about 625 nm), green light withwavelengths in a range of about 490 nm to about 570 nm (e.g., about 530nm), or blue light with wavelengths in a range of about 390 nm to about470 nm (e.g., about 455 nm). The diffraction gratings can includemultiple combinations and arrangements of protrusions and recessions(e.g., such as the protrusions 109 and the recessions 111) that togetherprovide desired optical effects. The diffraction gratings includein-coupling gratings and may form an orthogonal pupil expander regionand an exit pupil expander region. The functional pattern 208 has atotal length of about 10 mm to about 150 mm and a total width of about10 mm to about 150 mm.

The film coating 212 is also disposed along the interior region 216 ofthe substrate 202. The film coating 212 can provide the substrate 202with various properties or capabilities, such as abrasion resistance,improved surface hydrophobicity, color filtration, and brightnessenhancement. Example film coatings 212 include Zirconium Dioxide basedhard coats for chemical barrier coating and adding hydrophobicity and aTitanium Dioxide and Silicon Dioxide hard coating for abrasionresistance and use as inorganic based anti-reflective films. The filmcoating 212 may be applied to the substrate 202 via techniques such aslamination, slot-die coating, physical vapor deposition, evaporation,sputtering, and chemical vapor deposition.

The AR pattern 210 is imprinted (e.g., via the imprint lithographysystem 100) along the interior region 216 of the substrate 202 andsurrounding the functional pattern 208. The AR pattern 210 has a lengthof about 0.5 mm to about 150 mm and a width of about 0.5 mm to about 150mm. The AR pattern 214 is imprinted (e.g., via the imprint lithographysystem 100) across the film coating 212. The AR pattern 214 has a lengthof about 0.5 mm to about 150 mm and a width of about 0.5 mm to about 150mm. The AR patterns 210, 214 include AR features of a nano-scale thatmay be distributed in various quantities, arrangements, shapes, sizes,and orientations anywhere within the AR patterns 210, 214. AR featureswithin the AR pattern 210 may be either abutted seamlessly to thenearest diffraction grating of the functional pattern 208 or positionedat least about 5 μm from a nearest diffraction grating of the functionalpattern 208. The AR features are sized, arranged, and shaped to increaselight transmission (e.g., to reduce surface reflection) at the side ofthe substrate 202 on which the AR patterns 210, 214 are imprinted.

While FIGS. 3 and 4 illustrate a certain embodiment of an optical layer200, optical layers can include other arrangements of functionalpatterns, AR patterns, and film coatings. For example, FIG. 5illustrates a top view of an optical layer 500 that includes thesubstrate 202 and the functional pattern 208 of the optical layer 200,as well as an AR pattern 510. The functional pattern 208 is imprintedatop the upper side 204 of the substrate 202, as in the optical layer200. The AR pattern 510 is also imprinted atop the upper side 204 of thesubstrate 202 and is substantially similar in construction and functionto the AR pattern 210, except that the AR pattern 510 extends across theinterior region 216 to a peripheral edge 218 of the substrate 202.

In another example embodiment, FIG. 6 illustrates a top view of anoptical layer 600 that includes the substrate 202 and the functionalpattern 208 of the optical layer 200, as well as an AR pattern 610. Thefunctional pattern 208 is imprinted atop the upper side 204 of thesubstrate 202, as in the optical layer 200. The AR pattern 610 is alsoimprinted atop the upper side 204 of the substrate 202 and issubstantially similar in construction and function to the AR pattern210, except that the AR pattern 610 is provided as two separate regions640, 642 that surround separate portions of the functional pattern 208.

In another example embodiment, FIG. 7 illustrates a side view of anoptical layer 700 that includes the substrate 202, the functionalpattern 208 of the optical layer 200, and the AR pattern 214 of theoptical layer 200 without including the AR pattern 210 and the filmcoating 212. In the example optical layer 700, the AR pattern 214 isimprinted directly on the lower side 206 of the substrate 202.

In another example embodiment, FIG. 8 illustrates a side view of anoptical layer 800 that includes the substrate 202, the functionalpattern 208 of the optical layer 200, the AR pattern 210 of the opticallayer 200, and the film coating 212 of the optical layer 200 withoutincluding the AR pattern 214.

In another example embodiment, FIG. 9 illustrates a side view of anoptical layer 900 that includes the substrate 202, the functionalpattern 208 of the optical layer 200, the AR pattern 210 of the opticallayer 200, and the AR pattern 214 of the optical layer 200 withoutincluding the film coating 212. In the example optical layer 900, the ARpattern 214 is imprinted directly on the lower side 206 of the substrate202. In other embodiments, optical layers may include functionalpatterns and AR patterns with different shapes and/or arrangements notshown in the example optical layers 200, 500, 600, 700, 800, 900.

FIG. 10 provides scanning electron micrograph (SEM) images (a)-(d) ofexample AR features that may form the AR patterns 210, 214. For example,SEM image (a) illustrates AR features formed as free standing, isolatedprotrusions such as pillars 300. The pillars 300 can be cylindrical,polygonal prism, conical, tetrahedral or frustoconical in shape. Thepillars 300 have a height of about l0nm to about 300nm, a width of about10 nm to about 150 nm, and a pitch (e.g., a distance betweencorresponding points on adjacent, like elements) of less than about 200nm. SEM image (b) illustrates AR features formed as holes 302. The holes302 can be cylindrical, polygonal prism, conical, tetrahedral orfrustoconical in shape. The holes 302 have a depth of about 10 nm toabout 300 nm, a width of about 10 nm to about 150 nm and a pitch of lessthan about 200 nm. The pillars 300 and holes 302 may be distributed in ahexagonally closed packed array or a square packed array. SEM image (c)illustrates AR features formed as gratings 304 (e.g., elongatehorizontal bars having a length greater than a maximum width and amaximum height). The gratings 204 can be rectangular, frustoconical,ellipsoidal, or triangular in cross-sectional shape in a planeorthogonal to the direction of the gratings 304. The gratings 304 have aheight of about 10 nm to about 300 nm, a width of about 10 nm to about150 nm, and a pitch of less than about 200 nm. SEM image (d) illustratesAR features formed as discontinuous or short gratings or rods 306. Thesefeatures can be rectangular, frustoconical, ellipsoidal, or triangularin cross-sectional shape in a plane orthogonal to the direction of thelonger dimension axis. The features 306 have a height of about 10 nm toabout 300 nm, a width of about 10 nm to about 150 nm, a length greaterthan about 5 μm, and a pitch of less than about 200 nm. In general, ARfeatures of the AR patterns 210, 214 may have heights in a range ofabout 30 nm to about 300 nm, may have widths in a range of about 20 nmto about 100 nm, and may be distributed with pitches in a range of about50 nm to about 200 nm.

FIG. 11 illustrates effects of AR nanolayers applied (e.g.,) directlyatop a substrate (e.g., the substrate 202 or another substrate used toform optical layers in imprint lithography processes) according to aprocess such as nano-imprint lithography, photolithography, dry or wetetch, coat, lift-off, or lamination. Light passing from a first mediumof a first refractive index no to a second medium of a second refractiveindex n_(s) at a 0 degree incidence will be reflected at an interface ofthe first and the second mediums according to a reflectivity R given byEqn. 1 and transmitted through the second medium according to atransmissivity T given by Eqn. 2 (ignoring loss due to absorption,scatter, etc.). An optimal index of refraction n₁ of an intermediatelayer between the first and second mediums can be approximated from therefractive indexes of the first and second mediums according to Eqn. 3to produce low reflection loss at the interface. For example, Eqn. 1 isa general equation for reflection loss at a single interface (e.g., aflat interface) of a given index. Nanofeatures etched into such asubstrate will change the index of the surface and thus change thereflection loss. Therefore, in a general estimation, a single layer overa flat surface for reducing reflection loss has a general index that isgiven by Eqn. 3.

$\begin{matrix}{R_{s - 0} = {\frac{n_{s} - n_{0}}{n_{s} + n_{0}}}^{2}} & (1) \\{T = {1 - R}} & (2) \\{n_{1} = \sqrt{n_{0} \cdot n_{s}}} & (3)\end{matrix}$

For example, as shown in illustration (a), about 8.16% (R_(s-0)=0.0816)of light passing through air (n₀=1.0) and directly incident on thesubstrate (n_(s)=1.8) is reflected from the substrate, while about91.84% (T=0.9184) of the incident light is transmitted to the substrate.For light passing through air and incident on the substrate, the optimalindex of refraction n₁ for an intermediate layer at that interface isaround 1.34.

As shown in illustration (b), applying a flat nanoimprint 316 with athickness of less than 100 nm with a bulk index of refraction of 1.52(n=1.52) to the substrate causes a first amount of incident light (i.e.,4.26%) to be reflected at an interface between air and the flatnanoimprint 316 and causes a second amount of incident light (i.e.,0.71%) to be reflected at an interface between the flat nanoimprint 316and the substrate. The reflected amounts of light can be summed to givea total amount of light reflection loss of 4.97%. Thus, light passingthrough material 316 first requires the index at that air-materialinterface to be about 1.23, and applying the flat nanoimprint 316 to thesubstrate has reduced the reflectivity and increased the transmissivityof the substrate 202 by 3.19%. As shown in illustration (c), applying afeatured nanoimprint 318 (e.g., n=1.25) to the substrate causes a firstamount of incident light (i.e., 1.23%) to be reflected at an interfacebetween air and the featured nanoimprint 318 and causes a second amountof incident light (i.e., 0.65%) to be reflected at an interface betweenthe featured nanoimprint 318 and the substrate. The reflected amounts oflight can be summed to give a total amount of light reflection loss of1.89%. Thus, applying the featured nanoimprint layer 318 to thesubstrate has reduced the reflectivity and increased the transmissivityof the substrate by about 3%. In a general, AR features such as those ofthe featured nanoimprint 318 have an interface with air that has arefractive index in a range of about 1.24 to about 1.34.

Table 1 describes measured refractive indexes of film-air interfaces ofvarious film stack architectures that include nano-feature AR patternsalong with improved through transmission of light at a wavelength of 590nm. For example, a blank film of 100 nm thickness with a materialrefractive index of 1.52 over a transparent glass substrate ofrefractive index 1.78 gives a 4.25% improved transmission through thatinterface, when compared to the bare glass surface to air interface.When a blank film of higher refractive index 1.65 is used with similar100 nm thickness instead of a refractive index of 1.52, the reflectionloss is higher, and the net improvement is lower at 1.96% when comparedto the bare 1.78 index glass. However, when the films are stacked inwith the lowest index on top facing air and highest index 1.65 at theglass 1.78 interface, the reflection loss is lower, and improvement intransmission is 5.09% versus bare glass-air interface. This can be muchimproved if nanofeatures are fabricated with such material indices tobring the effective refractive index down to a more optimal level.

Patterning a single material (of index 1.52) with nanofeatures such aspillars of width of 50 nm, height of 100 nm and pitch of 100 nm in asquare array with a very thin (<50 nm) residual layer thickness(interconnecting material film for nanofeatures of same material), theeffective refractive index at the nanofeature material-air interface nowbecomes 1.28, which further improves transmission by 7.71% when comparedto bare glass-air interface. Similarly, if the material index was 1.65,then this effective refractive index at the nanofeature material-airinterface now becomes 1.32, thus improving transmission by 7.02% overbare glass-air interface. This type of embodiment is captured in FIG.12, where the low index material (e.g., 1.52) AR nano-feature 318 a isimprinted over a higher index material (e.g., 1.65) AR nano-feature 318b that is flush with the surface of the high index glass 1.78.

TABLE 1 Measured refractive indexes of film-air interfaces of variousfilm stack architectures. Measured Refractive Index Through %Transmission of surface open to Air Transmission at Improvement overDescription of Nanofilm Structure Layers over Substrate (n = 1) 590 nmBare Substrate Bare High Index Substrate (n = 1.78) 300 um thick w/BackNA 91.91% — side Inorganic AR Coating Blank Imprint Film (n = 1.52) 100nm thick on High Index 1.52 95.82% 4.25% Substrate (n = 1.78) 300 umthick w/Back side Inorganic AR Coating Blank Imprint Film (n = 1.65) 100nm thick on High Index 1.65 93.71% 1.96% Substrate (n = 1.78) 300 umthick w/Back side Inorganic AR Coating Blank Imprint Film (n = 1.52) 100nm thick over Blank Imprint 1.52 96.59% 5.09% Film (n = 1.65) 100 nmthick on High Index Substrate (n = 1.78) (Imprint over 1.65) 300 umthick w/Back side Inorganic AR Coating Imprint Geometry with 100 nmPitch 50 nm Diameter Pillar 1.28 99.00% 7.71% with n = 1.52 material onHigh Index Substrate (n = 1.78) (using 1.52 material) 300 um thickw/Back side Inorganic AR Coating Imprint Geometry with 100 nm Pitch 50nm Diameter Pillar 1.32 98.36% 7.02% with n = 1.65 material on HighIndex Substrate (n = 1.78) (using 1.65 material) 300 um thick w/Backside Inorganic AR Coating Imprint Geometry with 100 nm Pitch 50 nmDiameter Pillar 1.28 99.49% 8.25% with n = 1.52 material over ImprintGeometry with 100 nm (using pillar geometry Pitch 50 nm Diameter Pillarwith n = 1.65 material on High material 1.52 over pillar of IndexSubstrate (n = 1.78) 300 um thick w/Back side geometry material 1.65)Inorganic AR Coating

By further combining these two nano-feature imprinted films with thesame nano-pattern where the lower index material (1.52) film withnano-features is exposed to air and the residual layer of thenano-patterned higher index material (1.65) film touches the glasssurface (1.78) such that the residual layer thickness of the lower index(1.52) film covers the nano-features of the higher index material(1.65), the effective refractive index at the material-air interfaceremains 1.28, but the stack overall is more transmissive to light at a590 nm wavelength due to a gradual change of index as light propagatesthrough to the glass interface. For example, an improved transmittanceover the visible wavelength spectrum is shown in FIG. 13 a. FIGS.13b-13e also shows examples of a near optimally patterned nano-featurefilm surface with film thicknesses less than 130 nm and with pillar(refer to FIGS. 13 b, 13 c, and 13 e) and hole tone (refer to FIG. 13d )geometry, as compared to a standard anti-reflective multi-layer film(refer to FIG. 13f ), which can be several hundred nanometers of highand low index film coatings.

FIG. 14 illustrates a diagram (a) showing a substrate 400 withnanoimprint gratings 402 (blue) applied in a same direction asdiffraction gratings 404 (gray) of a functional pattern (wire gridpolarizer) on the substrate. The nanoimprint gratings 402 and thediffraction gratings 404 are located on opposite sides of the substrate400. FIG. 14 also illustrates a diagram (b) showing a substrate 400 withthe nanoimprint gratings 402 (blue) applied across (e.g., at an angle of90 degrees to) the diffraction gratings 404 (gray) of the functionalpattern. The nanoimprint gratings 402 and the diffraction gratings 404are located on opposite sides of the substrate 400.

FIG. 15 illustrates a graph plotting light transmitted through asubstrate with and without AR nanofeature type film. The grating type ARnanofeature imprint is applied to the back side of a WGP substrate wherethe grating of the AR imprint is orthogonal to the grating direction ofthe wire grid polarizer. As shown in the graph, applying the nanoimprintgratings in a direction across the direction of diffraction gratingsincreases the light transmission up to a wavelength of about 650 nm anddecreases the light transmission at wavelengths greater than about 650nm. The result illustrates a weak birefringence property when usinggrating type AR nanofeatures and applying such features in an orthogonaldirection to the polarized light exhibiting the WGP pattern as the lightencounters the AR gratings. Such features can reduce polarized lighttransmitted at higher wavelengths in such applications. This effect doesnot occur when using hole or pillar type AR nanofeatures. FIG. 16 showseffects with and without applying the grating type AR nanofeature alongthe WGP functional grating direction. It is shown that the lighttransmission increases overall over the visible spectrum by the gratingtype AR nanofeature imprint along the WGP.

The weak birefringence property exhibited by grating type AR nanofeaturefilm is also illustrated by the graph in FIG. 17. The graph shows thateffective surface refractive index of the grating type AR nano-featurechanges from 1.25 (across grating) to about 1.32 (along grating) basedon grating orientation to incoming linearly polarized light (provided byan ellipsometer) during refractive index measurement, which otherwisemeasures the refractive index of the material if a blank were to beimprinted as 1.52.

FIG. 18 shows a multi-layer wearable eyepiece 1300 having first opticallayer 1302, second optical layer 1302′, and third optical layer 1302″.First optical layer 1302, second optical layer 1302′, and third opticallayer 1302″ include first substrate 1304, second substrate 1304′, andthird substrate 1304″, respectively. First nanolayer 1306, secondnanolayer 1306′, and third nanolayer 1306″ are imprinted on firstsubstrate 1302, second substrate 1302′, and third substrate 1302″,respectively. First substrate 1302, second substrate 1302′, and thirdsubstrate 1302″ include first functional pattern 1308, second functionalpattern 1308′, and third functional pattern 1308″, respectively. In anembodiment of the optical layer AR pattern as applied to a multi-layerwearable eyepiece 1300, the AR pattern allows for more light to passthrough from a projection system to the input coupling diffractiongrating 1312 as light passes through multiple layers of the eyepiece.The AR pattern around the exit pupil diffraction grating 1314 allows formore world-side light to enter into the user's eye and reduces unwantedreflection or glare due to high reflectivity of the otherwise bare highindex glass surface in air.

FIGS. 19 and 20 respectively show example stacks 1100, 1200 of waveguideeye-pieces using a light source with a red color of wavelength 625 nm(a), a green color of wavelength 530 nm (b) and a blue color ofwavelength 455 nm (c) on one side of the stacks 1100, 1200. The stacks1100, 1200 includes six layers 1101 a-1101 f, 1201 a-1201 f(e.g., ofcolor red, blue, or green) located at different depths to which thelight has to travel. Each of the layers 1101 a-1101 f of the stack 1100include a substrate 1102, a blank imprint layer 1104 around a region ofinput coupling grating (ICG) (e.g., refer to the example optical layer600 of FIG. 6), and a non-imprinted AR nanolayer 1106. Each of thelayers 1201 a-1201 f of the stack 1200 include a substrate 1202, a blankimprint layer 1204 around a region of ICG, and an imprinted AR nanolayer1206. As shown, only about 81.7% of light intensity reaches the last redlayer 1101 f of the stack 1100 (i.e., with the flat AR nanolayer 1106),whereas about 95.6% of light intensity reaches the last red layer 1201 fof the stack 1200 (i.e., with the imprinted AR nanolayer 1206), suchthat the imprinted AR nanolayer 1206 provides a 13.9% absoluteimprovement in light intensity.

FIG. 21 displays a flow chart of an example process 1000 for configuringan optical layer (e.g., the optical layer 200, 500, 600, 700, 800, 900)in an imprint lithography process. One or more parameters of a nanolayer(e.g., the nanoimprint 210, 214, 316, 318, 510, 610) to be applied to asubstrate (e.g., the substrate 202, 400) for changing an effectiverefractive index of a substrate (e.g., a material-air interface on thesubstrate) are selected (1002). In some examples, the one or moreparameters include one or more of a shape, a dimension, and a materialformulation of the nanolayer. The nanolayer is imprinted on thesubstrate (e.g., the upper side 204 or the lower side 206 of thesubstrate 202) to change the effective refractive index of the substratesuch that a relative amount of light transmittable through the substrateis changed by a selected amount (1004). For example, a bare substratewithout any applied coating or nanoimprint may have an effectiverefractive index that is equal to an actual, bulk refractive index ofthe substrate. In some examples, applying the nanolayer changes theeffective refractive index from the actual, bulk refractive index to neweffective refractive index. In some embodiments, imprinting thenanolayer on the substrate to change the effective refractive index ofthe substrate includes changing a second relative amount of lightreflected from a surface of the substrate.

In some embodiments, the nanolayer is a flat nanoimprint (e.g., thenanoimprint 316). In some embodiments, the nanolayer is a featurednanoimprint (e.g., the nanoimprint 318). In some embodiments, thenanopattern includes AR features (e.g., pillars, holes, and/orgratings). In some examples, the AR features have a height in a range ofabout 10 nm to about 300 nm. In some examples, the AR features have awidth in a range of about 10 nm to about 150 nm. In some examples, theAR features are distributed with a pitch in a range of about 20 nm toabout 200 nm. In some embodiments, imprinting the nanolayer includesforming pillars (e.g., the pillars 300, 306, 308) on the substrate. Insome embodiments, imprinting the nanolayer includes forming holes 302 onthe substrate. In some embodiments, imprinting the nanolayer includesforming one or both of continuous gratings and discontinuous gratings(e.g., the gratings 314, 402) on the substrate.

In some embodiments, the process further includes forming a functionalpattern on a first side of the substrate and imprinting the nanolayeralong one or both of the first side of the substrate and a second sideof the substrate opposite the first side of the substrate. In someexamples, imprinting the nanolayer includes forming AR features of thenanolayer along a specific direction with respect to the functionalpattern the functional pattern. In some examples, imprinting thenanolayer includes forming AR features along a direction perpendicularto diffraction gratings of the functional pattern. In some embodiments,the process further includes applying a film coating (e.g., the filmcoating 212) to the substrate and imprinting the nanolayer atop the filmcoating.

In some embodiments, the process further includes changing the relativeamount of light transmitted through the substrate by about 0.5% to about15%. In some embodiments, the nanopattern is a first nanolayer, andprocess further includes imprinting a second nanolayer atop the firstnanolayer. In some embodiments, the process further includes changingthe effective refractive index to a first value based on the firstnanolayer and changing the effective refractive index to a second valuebased on the second nanolayer.

Advantageously, the process 1000 can be used to produce AR patterns thatmay reduce the surface reflection of a substrate by about 1% to about10%. Such AR patterns may increase the transmissivity of the substrateto greater than about 98% for a plastic substrate and up to about 9% fora glass substrate. The AR patterns may also provide the substrate with anew effective refractive index in a range of about 1.2 to about 1.4,such that transmission of light through the substrate is increased.Furthermore, the AR patterns discussed herein may introducebirefringence to diminish or enhance refraction of certain lightwavelengths transmitted through the substrate. In some implementations,weak birefringence can be advantageous if there is a need to modulatethe phase of light propagating within and through the substrate. Inaddition, at the specified dimensions of the AR nanopattern 214 and thefunctional diffraction patterns 208, the AR nanopattern 214 does notdiffract light as does the functional diffraction patterns 208. As aresult, the AR nanopattern 214 does not interfere with the diffractiveoptics of the optical device. Furthermore, the AR nanopattern 214provides an anti-stick surface that can maintain a certain predefinedgap in case two substrate layers in close proximity to each other shouldbe pushed against each other.

While the substrates discussed herein have been assumed to have arefractive index of about 1.78 to about 1.8, other substrates that maybe used in optical devices discussed herein may have a refractive indexin a range of about 1.45 to about 2.4.

While a number of embodiments have been described for illustrationpurposes, the foregoing description is not intended to limit the scopeof the invention, which is defined by the scope of the appended claims.There are and will be other examples, modifications, and combinationswithin the scope of the following claims.

(canceled)
 2. An optical layer, comprising: a substrate; and a nanolayerimprinted on the substrate, the nanolayer determining an effectiverefractive index of the substrate such that the nanolayer effects arelative amount of light transmittable through the substrate.
 3. Theoptical layer of claim 2, wherein the nanolayer is flat.
 4. The opticallayer of claim 2, wherein the nanolayer comprises features.
 5. Theoptical layer of claim 2, wherein the substrate comprises one or moreanti-reflective features.
 6. The optical layer of claim 5, wherein eachof the one or more anti-reflective features has a height in a range ofabout 10 nm to about 300 nm.
 7. The optical layer of claim 6, whereineach of the one or more AR features has a width in a range of about 10nm to about 150 nm.
 8. The optical layer of claim 5, wherein the one ormore anti-reflective features have a pitch in a range of about 20 nm toabout 200 nm.
 9. The optical layer of claim 2, wherein the substratecomprises pillars.
 10. The optical layer of claim 2, wherein thesubstrate comprises openings.
 11. The optical layer of claim 2, whereinthe substrate comprises one or both of continuous gratings anddiscontinuous gratings.
 12. The optical layer of claim 2, wherein afirst side of the substrate comprises a functional pattern, and thenanolayer is formed along one or both of the first side of the substrateand the second side of the substrate, wherein the second side of thesubstrate is opposite the first side of the substrate.
 13. The opticallayer of claim 12, wherein the nanolayer comprises an array ofanti-reflective features along a specific direction with respect to thefunctional pattern.
 14. The optical layer of claim 13, wherein theanti-reflective features of the nanolayer on the substrate areconfigured to change the effective refractive index of the substratebased on a direction of light propagation such that light transmittedthrough the substrate is changed by a selected amount.
 15. The opticallayer of claim 2, further comprising a film between the substrate andthe nanolayer.
 16. The optical layer of claim 2, where the optical layeris configured to change the relative amount of light transmittablethrough the substrate by about 0.5% to about 15%.
 17. The optical layerof claim 2, wherein the nanolayer is a first nanolayer, and furthercomprising a second nanolayer imprinted atop the first nanolayer. 18.The optical layer of claim 17, wherein the optical layer is configuredto change the effective relative index to a first value based on thefirst nanolayer and to change the effective refractive index to a secondvalue based on the second nanolayer.
 19. The optical layer of claim 17,wherein the substrate is a first substrate, the second nanolayer isimprinted on a second substrate, and the second substrate comprises afunctional pattern disposed along the second substrate.
 20. The opticallayer of claim 2, wherein the nanolayer is a first nanolayer, thesubstrate is a first substrate, and further comprising a second opticallayer comprising a second substrate and a functional pattern disposedalong the second substrate, wherein the first nanolayer is configured todetermine an effective refractive index of the first substrate such thatthe first nanolayer increases a relative amount of light transmittablethrough the first substrate to the second optical layer.
 21. The opticallayer of claim 20, wherein the functional pattern disposed along thesecond substrate is a first functional pattern, the optical devicefurther comprising a third optical layer comprising a third substrateand a second functional pattern disposed along the third substrate.